On Fri, Jun 7, 2013 at 1:11 AM, Junio C Hamano <gits...@pobox.com> wrote:
> The primary invariant of sort_in_topological_order() is to emit all
> children before their parent is emitted. When traversing a forked

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s/parent is/parents are/
> history like this with "git log C E":
>
> A----B----C
> \
> D----E
>
> we ensure that A is emitted after all of B, C, D, and E are done, B
> has to wait until C is done, and D has to wait until E is done.
>
> In some applications, however, we would further want to control how
> these child commits B, C, D and E on two parallel ancestry chains
> are shown. Most of the time, we would want to see C and B emitted
> together, and then E and D, and finally A, which is the default
> behaviour for --topo-order output.
>
> The "lifo" parameter of the sort_in_topological_order() function is
> used to implement this behaviour. After inspecting C, we notice and
> record that B needs to be inspected, and by structuring the "work to
> be done" set as a LIFO stack, we ensure that B is inspected next,
> before other in-flight commits we had known that we will need to
> inspect, e.g. E, that may have already been sitting in the "work to
> be done" set.
>
> When showing in --date-order, we would want to see commits ordered
> by timestamps, i.e. show C, E, B and D in this order before showing
> A, possibly mixing commits from two parallel histories together.
> When "lifo" parameter is set to false, the function keeps the "work
> to be done" set sorted in the date order to realize this semantics.
>
> But the name "lifo" is too tied to the way how the function implements
> its behaviour, and does not describe _what_ the desired semantics is.
>
> Replace the "lifo" field with an enum rev_sort_order, with two
> possible values: REV_SORT_IN_GRAPH_ORDER and REV_SORT_BY_COMMIT_DATE.
>
> The mechanical replacement rule is:
>
> "lifo == 0" is equivalent to "sort_order == REV_SORT_BY_COMMIT_DATE"
> "lifo == 1" is equivalent to "sort_order == REV_SORT_IN_GRAPH_ORDER"
>
> Signed-off-by: Junio C Hamano <gits...@pobox.com>
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